(i) Technical Field
A certain aspect of the embodiments discussed herein relates to semiconductor devices. Another aspect of the embodiments discussed herein relates to a semiconductor device having a multi-finger structure.
(ii) Related Art
As semiconductor devices suitable for amplification in RF bands such as microwaves, quasi-millimeter waves or millimeter waves, there is a known a field effect transistor (FET) such as a high electron mobility transistor (HEMI).
For example, Japanese Patent application Publication No. 8-172104 (Document 1) discloses an FET having a multi-finger structure having a plurality of gate fingers extending in parallel with each other, in which a source finger and a drain finger are respectively provided at opposite longitudinal sides of one gate finger so as to face each other across this gate finger.
The FET having the multi-finger structure has a source bus line interconnecting a plurality of source fingers, a drain bus line interconnecting a plurality of drain fingers, and a gate bus line interconnecting a plurality of gate bus lines. In an arrangement in which one source finger and one drain finger are opposite to each other across one gate finger, any of the source finger, the gate finger and the drain finger crosses any of the source bus line, the drain bus line and the gate bus line. For example, FIG. 1 of Document 1 discloses that the drain fingers and the source bus line cross each other.
In Document 1, in order to avoid a contact between the drain fingers and the source bus line, air bridges are provided in areas in which the drain fingers and the source bus line cross each other. However, the structure disclosed in Document 1 fails to realize a strong mechanical strength of the air bridges, and has a possibility that the air bridges may be crushed due to external force applied thereto.